1. Field of the Invention
The present invention relates to a reflective optical modulator.
2. Background Information
Such modulators are employed in optical data transmission systems in which a line end device generates the signal to be transmitted without having an available light source. The optical carrier for such a transmission signal in these systems is generated in a central station and is conducted to the line end device by way of an optical waveguide, is modulated there, and the resulting transmission signal is transmitted preferably over the same optical waveguide.
The publication entitled, Electronics Letters, May 8, 1986, Volume 22, No. 10, pages 517 and 518, discloses such a system which includes a reflective modulator. The disclosed reflective modulator is composed of an electro-optically active waveguide coupler which can be operated as a switch and is included in an integrated optical circuit.
The waveguide coupler has two branches each having two terminals. The optical waveguide for the transmission of data is disposed at a first terminal of the first branch and the reflective surface is disposed at a first terminal of the second branch. By way of suitable switching, light entering the modulator from the optical waveguide can be reflected back from the reflective surface into the optical waveguide. If one considers the light entering into the modulator as an optical carrier and the switching as modulation, it can be said that an optical transmission signal is generated by modulation of the carrier.
The drawback of the prior art reflective optical modulator is now that the adjustment between the optical waveguide and the integrated optical circuit in which the reflective modulator is disposed must be very accurate and is therefore correspondingly expensive from a technology aspect.